Imaging system with an integrated source and detector array

ABSTRACT

An imaging system with an integrated source and detector array. A plurality of light detectors are arranged in an array and a corresponding plurality of light sources are arranged in an array in an epi-illumination system so that light radiated from a point on the object illuminated by a given source is detected by a corresponding detector. An optical system is disposed so as to illuminate an object with light from the source array and image the object on the detector array. Ordinarily, the sources and detectors are coplanar and, preferably, are fabricated or at least mounted on the same substrate. In one embodiment the Airy pattern of the point response of the optical system encompasses both a detector and corresponding light sources. In another embodiment, the optical pathway is split by a diffractive element to produce conjugate points corresponding to light sources and their respective detectors. In a further embodiment, the pathway is split by a Wollaston prism. In yet another embodiment where the illumination and image light have different wavelengths, the pathway is split by dispersion. Another embodiment comprises a power supply connected to the plurality of light sources, a signal conditioning circuit for receiving and digitizing output signals from the light detectors so as to produce a respective set of output values, and an equalizing system for equalizing the output values for a given input radiance.

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 10/158,633, filed May 30, 2002, which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0002] This invention relates to illumination for optical imagingsystems, particularly to an integrated detector and source array forepi-illumination in an imaging system, and more particularly inminiature microscope arrays.

BACKGROUND OF THE INVENTION

[0003] In an imaging system, adequate and appropriate illumination ofthe object to be imaged is essential. There must be enough lightprovided to the object to permit a viewer or detector to discernfeatures of the object in the image thereof. In addition, the manner inwhich the light is provided to the object makes a difference in whatfeatures can be detected and the contrast with which they are imaged.

[0004] The way in which illumination is provided is particularlyimportant in a microscope. If the object is opaque, it must beilluminated so that the light used to form an image of the object isradiated from the same side of the object on which light illuminates theobject. This type of illumination is known primarily asepi-illumination. In epi-illumination the light radiated from an objectmay be in the form of reflection, in which case the illumination lightis modulated upon reflection from the object, or it may be in the formof fluorescence, in which case the illumination light inducesfluorescent emission by the object at a different wavelength from theillumination light, as determined by the fluorescence characteristics ofthe object. The latter case is known as epi-fluorescence. The term“radiated” is used throughout this specification and the claims hereofto include reflection, scattering and fluorescence.

[0005] One type of epi-illumination is critical illumination. In thiscase, the light source is imaged into the object plane. This providesefficient illumination and a short illumination system, but requiresthat the light source provide uniform radiance. The light source isordinarily disposed actually or virtually on the optical axis of theimaging lens.

[0006] In the foregoing it is assumed that the entire field of view ofthe imaging lens is simultaneously imaged. However, in a confocalmicroscope only discrete points in object space are imaged. This isaccomplished by placing one or more “pinhole” stops at the image planeof the microscope matched to corresponding discrete points in the objectplane, and scanning the object laterally, either by moving the object orthe microscope, or moving the scanning beam through the microscopeusing, for example, scan mirrors. The light passed by the pinhole isdetected and related to the object position as the scan occurs, and theoutput of the detector is used to produce an image of the object as awhole. In this case, light from the light source is focused to the pointon the object plane that is currently imaged. This is typicallyaccomplished by placing a beam splitter between the imaging lens and theimage plane so as to pass image light to the image plane whilereflecting source light from a virtual image plane created by the beamsplitter along the optical axis of the microscope toward the objectplane.

[0007] In classic optical instruments employing critical illumination,the image is detected by the human eye. In many modern opticalinstruments, the image is detected by a photo-sensitive device,typically an array of photodetectors. In confocal microscopy, the imageis necessarily detected by a photodetector. While the use of electronicimage detection offers electronic capture of an image and thepossibility of reducing the size of an imaging system, effective,compact epi-illumination has remained a challenge.

[0008] The recent development of miniaturized microscope arrays presentsnew challenges for illumination. In a miniature microscope array aplurality of laterally-distributed optical imaging elements havingrespective longitudinal optical axes are configured to image respectivesections of a common object, or a plurality of respective objects anddisposed with respect to a common object plane, so as to produce imagesthereof at respective image planes. The individual lenses of this arrayare formed of small optical elements, or “lenslets,” that place severeconstraints on providing illumination. Indeed, the multiplicity oflenslets arranged in an array and the small dimensions of the arraysuggest that prior art epi-illumination techniques cannot be used. Yet,a principal application for miniature microscope arrays is to imagespecimens, such as biological microarrays for protein analysis, that aresufficiently opaque that trans-illumination cannot be used effectively.

[0009] In a miniaturized microscope array each of the microscopes has atleast one, and ordinarily many, optical detectors associated therewithfor producing an electrical representation of the image produced by themicroscope. The detectors are most likely to be semiconductor opticaldetectors. Each microscope may also have an illumination sourceassociated therewith.

[0010] The electrical output of a semiconductor optical detector inresponse to a given radiance depends on its responsivity as well as theamount of radiant flux that actually reaches the active area of thedetector. Such detectors typically produce a DC offset component intheir output due to dark current, as well as a signal that varies withthe radiant flux received by the detector. The responsivities and DCoffsets of detectors may vary from detector to detector, even though thedetectors may be the same kind of device. Consequently, where multipledetectors are employed as in an array microscope, the respectivedetectors may produce different electrical output amplitudes andoffsets, even when illuminated by the same radiant flux. Similarly, theoutput radiances of optical sources may vary from source to source, eventhough the sources may be the same kind of device and may experience thesame input current or voltage. Consequently, where multiple sources areemployed to provide illumination for respective detectors, therespective detectors may receive varying light radiances, all otherthings being equal. These variations in source radiance and detectorresponsivity and flux-dependent DC offset can create pixel-to-pixelbrightness errors in the images produced by a microscope array.

[0011] Accordingly, there is a need for novel systems and methods forproviding critical illumination in epi-illumination imaging systemsemploying electronic image detection, and for equalizing the response ofan imaging system over the entire image to an object whose radianceresponse to a given irradiance is uniform over the entire object.

SUMMARY OF THE INVENTION

[0012] The present invention meets the aforementioned need by providing,in an imaging system, a plurality of light detectors arranged in adetector array and a plurality of light sources corresponding todetectors in the detector array, so that light radiated from a point onthe object illuminated by a given source of the source array is detectedby a corresponding detector of the detector array. An optical system isdisposed with respect to the detector array and the source array so asto illuminate an object with light from the source array and image theobject on the detector array. Corresponding detectors and sources aredisposed in back of the optical system and preferably interspersed amongone another. Ordinarily, the sources and detectors preferably arecoplanar, and preferably are fabricated or at least mounted on the samesubstrate. One or more sources may have a plurality of correspondingdetectors, and one or more detectors may have a plurality ofcorresponding sources.

[0013] In one embodiment the Airy pattern point response of the opticalsystem encompasses both a detector and its corresponding light sources.In another embodiment, the optical pathway is split by a diffractiveelement to produce conjugate points coupled to sources and theirrespective detectors. In a further embodiment, the pathway is split by aWollaston prism or other polarizing element. In yet another embodimentwhere the illumination and image light have different wavelengths, thepathway is split by dispersion. The system is particularly suited forfluorescence imaging, confocal microscopy and array microscopes.

[0014] Another embodiment of the invention comprises a power supplyconnected to a plurality of light sources for supplying power thereto, asignal conditioning circuit for receiving and digitizing output signalsfrom a respective set of light detectors so as to produce a respectiveset of output values, and an equalizing system for equalizing arespective set of output values for a given amount of input powersupplied thereto by said source. In one method, the equalizing system isadapted to add to one or more of the output values a respective errorcorrection value so as to produce new respective values that aresubstantially equal for the given amount of input power. In anothermethod the signal conditioning circuit includes a set of amplifierscorresponding to said set of said plurality of light detectors whichapply gain to said output signals prior to digitization thereof, and theequalizing system provides correction signals to the amplifiers based onthe output values so as to equalize the output values for the givenamount of input power. The amplifiers or associated analog-to-digital(“D/A”) converters may be adapted to adjust their gain and offset inresponse to the correction signals. In addition, the power supply may beadapted to supply to the plurality light sources respective amounts ofpower that have definite relative magnitudes with respect to oneanother, and the equalizing system is adapted to equalize the outputvalues taking into account the relative amounts of power supplied to theplurality of light sources.

[0015] What is meant by “equalization” herein is equalizing the responseof the imaging system, including sources and detectors and, whereappropriate, the electronic interface, over the entire image to anobject whose signal response to a given object properties is uniformover the entire object. Then, an equalized image is one whose relativebrightness values over the entire surface thereof depend on thecorresponding surface radiance responses of the object, not on thesource irradiance or detector responsivities or offsets.

[0016] Accordingly, it is a principal objective of the present inventionto provide novel systems and methods for imaging and illumination in amulti-axis imaging system.

[0017] The foregoing and other objectives, features, and advantages ofthe invention will be more readily understood upon consideration of thefollowing detailed description of the invention, taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1(a) is an axial view of a two-dimensional integrated sourceand detector array according to the present invention.

[0019]FIG. 1(b) is an axial view of a one-dimensional integrated sourceand detector array according to the present invention.

[0020]FIG. 1(c) is an axial view of a one-dimensional integrated sourceand detector array, wherein more than one light source is associatedwith a given detector, according to the present invention.

[0021]FIG. 2 is a side view and intensity-distribution diagram of animaging system employing an integrated source and detector array inaccordance with the present invention, wherein both the source and thedetector lie within a predetermined portion of the Airy pattern of thepoint response of an imaging system.

[0022]FIG. 3 a side view and ray trace diagram of an imaging systememploying an integrated source and detector array according to thepresent invention, wherein a diffractive element is employed to produceconjugate points in image space.

[0023]FIG. 4 is a side view and ray trace diagram of an imaging systememploying an integrated source and detector array according to thepresent invention, wherein a Wollaston prism is employed to produceconjugate points in image space.

[0024]FIG. 5 is a side view and ray trace diagram of a fluorescenceimaging system employing an integrated source and detector arrayaccording to the present invention, wherein a direct view prism isemployed to produce conjugate points in image space.

[0025]FIG. 6 is a side view and ray trace diagram of a confocal imagingsystem employing an integrated source and detector array according tothe present invention, wherein a diffractive element is employed toproduce conjugate points in image space.

[0026]FIG. 7 is a perspective view of an illustrative array microscopeincorporating an integrated source and detector array according to thepresent invention.

[0027]FIG. 8 is a block diagram of a first embodiment of a microscopearray system including a circuit to equalize the outputs of detectorsfor a given irradiance illumination, in this case by adjusting the powerapplied to respective light sources and computationally correcting themeasured image brightness values.

[0028]FIG. 9 is a block diagram of a second embodiment of a microscopearray system including a circuit to equalize the outputs of detectorsfor a given irradiance illumination, in this case by adjusting the powerapplied to respective light sources and providing gain and offset valuesto a video board.

[0029]FIG. 10 is a block diagram of a third embodiment of a microscopearray system including the equalization of the outputs of detectors fora given irradiance illumination, in this case by adjusting the powerapplied to respective light sources and modifying the gain and offset ofindividual amplifiers associated with each detector of a detector array.

[0030]FIG. 11(a) is a flow chart of a method for computing and storingbrightness equalization values for calibration.

[0031]FIG. 11(b) is a flow chart of a method for equalizing imagebrightness by computationally correcting the measured image brightnessvalues.

[0032]FIG. 11(c) is a flow chart of a method for equalizing imagebrightness by applying gain factors and DC offset corrections to a videoboard or set of amplifiers.

[0033]FIG. 11(d) is a flow chart of a method for equalizing imagebrightness by adjusting the power applied to individual illuminationlight sources.

[0034]FIG. 12(a) is a side view and ray trace diagram of an exemplaryembodiment of a multi-axis, trans-illumination, multi-axis imagingsystem in which the equalization features of the present invention maybe used.

[0035]FIG. 12(b) is a side view and ray trace diagram of an exemplaryembodiment of a single-axis, trans-illumination, multi-axis imagingsystem in which the equalization features of the present invention maybe used.

DETAILED DESCRIPTION OF THE INVENTION

[0036] In a modern imaging system having electronic image detection, theimage is typically detected by an array of photodetectors disposed inthe image plane of the imaging system. The array may be two-dimensionalor one-dimensional. In any event, each photodetector is customarily thesource of one pixel of data, though in the case of a color imagingsystem where one photodetector is provided for each color to be detectedone pixel may have multiple photodetectors associated with it. Thepresent invention employs such an array of photodetectors, animprovement being that light sources may be interspersed in the arrayamong the photodetectors. In this case, each pixel has one or more lightsources, as well as one or more photodetectors, associated with it.Preferably, the sources and detectors are coplanar and, preferably,fabricated or at least mounted on the same substrate; however, for someapplications the sources and detectors may lie in different planes.While the light sources preferably are disposed between the detectors,the principles of the invention could also be applicable to situationswhere the sources and detectors overlap or even lie substantially on thesame axis.

[0037] FIGS. 1(a), 1(b) and 1(c) show exemplary integrated photodetectorand light source arrays according to the present invention. In FIG. 1(a)a two-dimensional array 10 of integrated photodetectors 12 and lightsources 14 is shown, each photodetector having a light source associatedtherewith as shown by circle 16. The individual photodetectors 12 may beany practical opto-electonic photo-sensitive device small enough toprovide the desired image resolution, such as CMOS photodiodes, as iscommonly understood in the art. The light sources 14 are preferablylight-emitting diodes or laser diodes, depending on the type ofillumination desired. Vertical cavity emitting semiconductor lasers areparticularly suitable for this invention because they emit lightperpendicular to their substrate and can produce unpolarized light.However, other light emitting devices small enough to fit within thearray may be used, whether they are semiconductors, lasers or not,without departing from the principles of the invention.

[0038] In FIG. 1(b) a one-dimensional integrated array 18 is shown whereeach photodetector 12 has only one light source 14 associated with it,as in FIG. 1(a). However, there may be applications which call for twoor more light sources 14 associated with a single photodetector 12 in anintegrated array 20, as shown in FIG. 1(c).

[0039] Turning to FIG. 2, a first embodiment 22 of a one-dimensionalintegrated source and detector array epi-illumination system takesadvantage of the diffraction-limited point response function of anoptical system to provide both illumination and detection of the lightat a point on an object to be imaged. An optical system 24 has anoptical axis 26, an object plane 28 and an image plane 30. The opticalsystem may be a single or multiple element system, a refractive elementsystem, a reflective element system, a diffractive element system, orsome combination of the foregoing, as appropriate for the particularapplication. In any case, the optical system produces an image 32 at theimage plane of a point 34 on the object plane, the image of the pointrepresenting the impulse (point) response, or point spread function(“PSF”), of the optical system. The PSF will depend on the wavelength,the aperture of the optical system and the aberrations of the opticalsystem. To the extent the system can be corrected to render theaberrations insignificant, the image will be effectively diffractionlimited. In the case of a circularly symmetric aperture, the PSF willthen be an Airy pattern, a two-dimensional cross section of which isshown as image 32 in FIG. 2. The source 34 and detector 36 can bepositioned so that the central lobe 38 of the PSF covers both the sourceand the detector, provided that both the source and the detector aresmall enough, without spreading a significant amount of energy into anadjacent source and detector pair. In this manner, the source anddetector act as a single point to the optics.

[0040] While this first embodiment does not provide optimal lightefficiency, it is simple, compact, and straightforward to manufacture.It can be implemented with either a one-dimensional array, as shown inFIG. 1(b) or a two dimensional array, as shown in FIG. 1(a). To increaselight efficiency, multiple detectors surrounding the light source withinthe central lobe of the image could be used. Also, the optical systemcan be designed to have desired aberrations so as to produce anon-symmetric PSF and maximize the light irradiating the detector area.As will be understood by a person skilled in the art, there are variousways of accomplishing this, including, for example, forming lenses withaspherical surfaces and decentering the elements of the optical system.

[0041] A second embodiment 40 of a one-dimensional integrated source anddetector array illumination system, shown in FIG. 3, uses a diffractionelement to separate the illumination light from the image light at imageplane. As in FIG. 2, the system has an optical system 24, with anoptical axis 26, and object plane 28 and an image plane 30. A source 34and detector 36, which are part of a linear array, are preferablydisposed symmetrically about the optical axis at the image plane 30. Inthis case, a diffraction element 42 is also included. The diffractionelement, which may be, for example, a grating or hologram, is preferablyoptimized to maximize the diffraction efficiency of the +δ and −δ firstdiffraction orders, while minimizing the diffraction efficiency of allother orders. The source and detector are then placed in the respectivepaths of those two orders, that is, coupled thereto, so that the sourceand detector are conjugate to one another and thereby provide optimumuse of light.

[0042] In a third embodiment, conjugate points on the image plane can beformed by a Wollaston prism. As shown in FIG. 4, a quarter wave plate 44may be placed in front of a Wollaston prism 46 at an angle to the twoeigenaxes thereof so that the optical pathway is split into two pathwayshaving respectively orthogonal polarizations and respective angles ofrefraction, as indicated by the dot 48 and arrow 50. This requireseither that the source 36 produce light that is linearly polarized inthe direction represented by dots 48, or that a linear polarizer 49 beused to produce such linear polarization. The source light is thencircularly polarized in one direction by the quarter wave plate,circularly polarized in the opposite direction upon reflection from theobject, then linearly polarized in the direction of arrows 50 by thequarter wave plate. Thus, this arrangement creates two conjugate pointsin the image plane that correspond to a light source 34 andphotodetector 36, respectively.

[0043] In the case of fluorescence imaging, the dispersive qualities ofoptical elements can be employed to produce conjugate points in imagespace. In fluorescence imaging the light source has a first wavelength,or more generally a first energy spectrum, that excites the object tofluoresce and thereby emit light at a different wavelength, or moregenerally a different energy spectrum. In this case, the light sources34 emit light at one wavelength, typically an ultra-violet wavelength,and the photo-detectors 36 either are sensitive to a differentwavelength or associated with filters that limit the spectrum receivedthereby to a different wavelength. For example, a direct vision prism 52splits the optical pathway 54 into two branches corresponding to theexcitation and fluorescence emission wavelengths, respectively, as shownin the embodiment of FIG. 5. Thus, it creates two conjugate points inthe image plane that correspond to a light source 34 that emits light atone wavelength and photo-detector 36 that is responsive to anotherwavelength. A number of detectors can be used as well to detect lightcorresponding to a corresponding number of different wavelengths, suchas red, green and blue light.

[0044] Generally, any device that conjugates spatially-separated pointscorresponding respectively to light sources and photo-detectors in imagespace for epi-illumination may be used without departing from theprinciples of the invention.

[0045] While the light source array and photodetector array areordinarily coplanar for producing critical illumination, they can bedisposed in axially separate planes. This may be desirable, for example,to compensate for axial dispersion in fluorescence imaging. In thatcase, the array of light sources is placed at the image plane for theexcitation light, while the photodetector array is placed at the imageplane of the wavelength of light to be detected.

[0046] The embodiments of FIGS. 2-5 can also be used in a confocal mode,as shown with respect to the second embodiment in FIG. 6. In this case,a stop is provided with an array of pinhole apertures 54, one for eachdetector 34, and with conjugate apertures for the light sources 36. Theimage of each source, which is essentially a point source, is conjugatedwith the object plane. After reflection from the object, the light isimaged onto a corresponding pinhole aperture 54. The amount of lightthat passes through the aperture is closely related to the focus of theimage and can be used to gauge the distance of the object surface to thefocal position. If the object and the light beam are then moved withrespect to one another, the profile of the object can thereby bedetermined. By providing a linear array of source-detector pairs andscanning the object in a direction perpendicular to the array, rapidconfocal scanning can be achieved. Depending on the sources anddetectors, the exit apertures of the sources and the active areas of thedetectors may be small enough to eliminate the need for the array ofpinhole apertures 54.

[0047] The embodiments of FIGS. 2-6 can be employed in a miniaturizedmicroscope array, or more specifically an array microscope, as shown inFIG. 7. An exemplary embodiment of an array microscope 56 comprisespluralities of lenses 58, corresponding to individual microscopeelements, disposed on respective lens plates 60, 62 and 64, which arestacked along the optical axes of the microscope elements. An array 66of linear, integrated source-detector arrays 68 resides above the lastlens plate. The array microscope 66 is typically employed to scan asample on a carriage 70 as the carriage is moved with respect to thearray or vice versa. Each set of corresponding lenses 58 and respectivelens plates 60, 62 and 64 images a section of the object onto acorresponding source-detector array 58 as the object moves by on thecarriage 70.

[0048] Since the individual elements of a light source array may vary intheir radiance characteristics, and individual elements of a detectorarray may vary in their offset and responsivity characteristics, thepresent invention contemplates several approaches to equalization ofimage brightness for a uniform object irradiance characteristic. Theseapproaches may complement one another or be used in the alternative. Ingeneral, one approach is to process digitally the numericalrepresentations of image intensity so as to compensate mathematicallyfor variations in dynamic range and offset of the detector outputs basedon stored knowledge of the individual response characteristics. Anotherapproach is to adjust the dynamic range of the detectors by adjustingeither the powers of their respective light sources or the gains oftheir respective amplifiers, or both, and to compensate for differentdetector offsets by adjusting the offsets of their respective amplifiersor A/D converters, or both.

[0049] Referring to FIG. 8, one approach to equalization is toselectively add correction values to image brightness values mapped toan image produced by a microscope array. In FIG. 8, the microscope arrayis represented schematically at 70 by a plurality of light sources 72and corresponding light detectors 74, the presence of epi-illuminationand imaging optics as described above being implied. Power is suppliedto the light sources 72 by a power supply 76, and the analog signaloutputs from the detectors are provided to a video card 78, whichsamples and converts those signals to digital representations ofbrightness values mapped to image pixels, as is well known in the art.The power supply may be adapted to direct a selected amount of power torespective individual light sources 72. The detector brightness valuesare provided to a digital processor 80, which may perform processingoperations on those values, store those values in a memory 82, providethose values to an output interface 84, perform some combination of theforegoing three functions, or perform some other function for which theprocessor is constructed or programmed.

[0050] In the case where substantially the same amount of power isprovided to all, or a known set, of the light sources 72, and an objectof uniform radiance response is illuminated and imaged, the processor 80is adapted to compute and add to selected brightness valuescorresponding correction values that produce a resulting image ofuniform brightness. The amount of power may be applied to the sourcesmay be fixed or set by the processor via bus 86 between the power supply76 and the processor 80. What is meant by an object of uniform radianceresponse is a two dimensional surface whose reflectance or transmittanceis essentially the same over the entire field of view of the arraymicroscope. In addition, or as an alternative, to correcting thebrightness values, the processor 80 may be architecturally adapted orprogrammed to provide a first set of correction signals to the powersupply via bus 86 so as to adjust the individual radiances forrespective sources 72 to achieve equalization.

[0051] The correction values may correct for variations in gain oroffset of the detectors and their associated electronics, and forvariations in radiance of the sources. The processor may either computethe correction required for each brightness value produced by a detectorbased on a mathematical model of the response of the detector, or it mayutilize a look-up table of calibrated or pre-computed correction values,as is well understood in the art. In addition, or in the alternative,the processor may use correction values to provide a desired non-linearbrightness response to the detected radiance from the object, forexample, to compress a large dynamic range in radiance logarithmically.

[0052] Turning to FIG. 9, a video board 90 may be employed which acceptsa correction signal input so as to adjust the gain and offset of theelectronics that convert the analog output of the detectors to a digitalvalue representative of image pixel brightness. The processor 80 may bearchitecturally adapted or programmed to provide a first set ofcorrection signals to the power supply via bus 86 so as to adjust theradiances for respective sources 72, or to provide sets of gain oroffset correction signals to the video card 90 via bus 92, or somecombination of the foregoing, in response to the brightness valuesproduced by the video card to equalize those brightness values for anobject of uniform radiance response. The video card 90, which containsboth detector amplifiers and A/D converters, may be architecturallyadapted or programmed to effectuate the required gain and offsetcorrections, for example by the use of discrete logic or afield-programmable gate array and digital-to-analog converters, byconverting the digital commands of the processor 80 to a set of analogsignals to the amplifiers to set their individual gains and to the A/Dconverters to set their offset.

[0053] In FIG. 10, a set of amplifiers 94 and a set of D/A converters96, corresponding and responsive to respective detectors 74, areprovided instead of a video card, the amplifiers providing analog signalconditioning and gain and the D/A converters being adapted to sample anddigitize the outputs of the amplifiers so as to provide digital wordsrepresentative of brightness values. In this case, the correctionsignals more directly act on the amplifiers 94 via bus 93 and A/Dconverters 96, via bus 95, the amplifiers and A/D converters havingtheir own digital-to-analog conversion circuitry.

[0054] In one embodiment, there is an amplifier for each detector, thatis, for each pixel of the image that is produced, which requires largescale integration of amplifiers with the detectors. In anotherembodiment the requirement for so many amplifiers is reduced by takingadvantage of the fact that the intensity signals generated by theindividual detectors are shifted out of a CCD array serially, row ofdetectors-by row. Only one amplifier for each row is needed in thisembodiment where the gain of each amplifier is synchronously set foreach detector as the detector's signal passes there through.

[0055] Method flow charts for processor operation are shown in FIGS.11(a)-11(d). The processor may be architecturally adapted to carry outthe operations of the flow charts, or may be programmed to carry outthese methods. In either case, it is to be understood that these areexemplary functions and that variations on the steps shown in the flowcharts, and even other functions, may be implemented by the processorwithout departing from the principles of the invention.

[0056] Referring first to FIG. 11(a), in a preferred embodiment, beforean actual specimen is scanned, in step 100 the outputs of the detectors74 are measured without any illumination and those outputs are stored,in step 102, as detector offset values. In step 104, a first knownamount of calibration power Φ_(1n) is supplied to the light sources 72,and in step 106 the outputs of the detectors 74 are stored as firstdetector calibration values C_(1n). In step 108, a second known amountof calibration power Φ_(2n) is supplied to the light sources 72, and instep 110 the outputs of the detectors 74 are stored as second detectorcalibration values C_(2n). Based on the first and second calibrationpowers and corresponding first and second calibration values, theresponsivities of the array of detectors are computed in step 112 asfollows:

R _(n)=(C _(2n) −C _(1n))/(Φ_(2n)−Φ_(1n))

[0057] where n indicates a plurality of responsivity valuescorresponding to respective detectors in the array 74, and responsivityis used loosely to refer to the detector electrical response to theelectrical power input to its corresponding light source, rather thanthe radiant flux input to the detector itself, it being recognized thatnot all the electrical power input to a source will become radiant powerreceived by the corresponding detector. Based on these responsivity andoffset measurements, gain factor and offset correction values aredetermined in step 114.

[0058] While the flow chart in FIG. 11(a) shows preferred calibrationsteps, the flow chart in FIG. 11(b) show the method that wouldpreferably be used to equalize a system by correcting measuredbrightness values. Thus, in step 200, when an object is scanned imagebrightness values are produced by the video card 78. In step 202, theprocessor retrieves stored gain and offset correction values, found inthe manner described for FIG. 11(a). The processor then computes newbrightness values in step 204 by multiplying the brightness value by acorrection factor and adding an offset correction value, which may benegative. In step 206, the new image brightness values thus computed arethen stored as an equalized image.

[0059]FIG. 11(c) illustrates a method for equalization where a videocard 90 or a set of amplifiers94 and corresponding A/D converters 96 isadapted to receive digital gain and offset correction values. In thiscase, once calibration has been accomplished in accordance with theprocess represented by FIG. 11(a), the stored gain and offset correctionvalues are retrieved in step 300 and applied to the video card 90 oramplifiers 94 and A/D converters 96 in step 302. Where a plurality ofamplifiers and respective A/D converters corresponding to each detectorare provided, the gain and offset values are set in parallel. Where onlyon amplifier is provide for each row of detectors is provided, the gainadjustments are made dynamically, in synchronism with the serial readoutof intensity values produced by the detectors. A specimen is thenscanned and its image is captured by the detectors 74. The outputs ofthe detectors are then acquired in step 304 so as to provide anequalized image.

[0060]FIG. 11(d) illustrates a method of equalization by adjusting thepower supplied to the light sources. Thus, in step 400, the stored gainand offset correction values are retrieved. These values are then usedto set the individual powers supplied to respective light sources 72, instep 402, to equalize the detector responsivities. Lastly, a specimen isscanned with the powers set, and the brightness values of the image areacquired and stored in step 404. It is to be understood that, while theprocesses of FIGS. 11(b), 11(c) and 11(d) are shown separately, inaccordance with the invention they may be use in any practical andconvenient combination to provide equalized images.

[0061] While the equalization system described above was first describedin the context of an epi-illumination system with integrated sources anddetectors because it is particularly useful in such a system, theprinciples of the equalization system are also adaptable to a anepi-illumination imaging system without integrated sources anddetectors, a trans-illumination imaging system.

[0062]FIG. 12(a) shows an exemplary embodiment of a multi-axis,trans-illumination, multi-axis imaging system 406. In this system anarray 408 of independently-powered light sources 410 (1−n) is provided.Each of the sources is imaged to a corresponding point on the specimen412 by a respective lens 414 (1−n) of condenser array 416. Theillumination light is transmitted through each respective point, withvarying respective degrees of absorption, and is thereafter imaged byrespective lenses 418 (1−n) of a microscope lens array 420 to respectivedetectors 422 (1−n) of microscope detector array 424. For convenience,in FIG. 12(a) the vertical extend of the components of this system havebeen shortened, it being understood that much larger arrays of sources,lenses and detectors would be used in practice. In this embodiment, thepower to the individual sources may be adjusted individually, just asdescribed above with respect to epi-illumination, to equalize theoutputs of the detectors and associated electronics.

[0063] An exemplary single-axis, trans-illumination, multi-axis imagingsystem 426 is shown in FIG. 12(b). In this embodiment, the imaging sideis the same as the imaging side of system 406. However, the illuminationside comprises a single, extended source 428, and a telecentricillumination system having a condenser lens 430 with focal length “f”.As in FIG. 12(a), the vertical extents of the components of the systemillustrated by FIG. 12(b) have been shortened from what would be used inpractice. As can be seen, each point on the specimen 412 is illuminatedwith a numerical aperture the same as the numerical aperture of theimaging side 406. Various single-axis trans-illumination systems for amulti-axis imaging system are described in copending U.S. patentapplication Ser. No. 10/191,874, filed Jul. 8, 2002, the entire contentsof which are hereby incorporated by reference.

[0064] The terms and expressions which have been employed in theforegoing specification are used therein as terms of description and notof limitation, and there is no intention, in the use of such terms andexpressions, to exclude equivalents of the features shown and describedor portions thereof, it being recognized that the scope of the inventionis defined and limited only by the claims which follow.

We claim:
 1. An imaging system, comprising: a plurality of lightdetectors arranged in a detector array; a plurality of light sourcescorresponding to detectors in the detector array and arranged in asource array; and an optical system disposed with respect to the sourcearray and the detector array so as to illuminate an object with lightfrom the source array and image the object on the detector array,corresponding detectors of the detector array and sources of the sourcearray being disposed in back of the optical system and being arranged sothat light radiated from a point on the object illuminated by a givensource of the source array is detected by a corresponding detector ofthe detector array.
 2. The imaging system of claim 1, wherein thedetector array and the source array are coplanar with one another. 3.The imaging system of claim 1, wherein the detector array and the sourcearray are not coplanar with one another.
 4. The imaging system of claim1, wherein one or more sources in the source array has a plurality ofdetectors in the detector array that correspond thereto.
 5. The imagingsystem of claim 1, wherein one or more detectors in the detector arrayhas a plurality of sources in the source array corresponding thereto. 6.The imaging system of claim 1, further comprising an optical elementdisposed between the optical system, on the one hand, and the detectorsand sources, on the other hand, to produce conjugate points in imagespace coupled respectively to corresponding sources and detectors. 7.The imaging system of claim 6, wherein the optical element comprises adiffractive element optimized to maximize energy in diffraction ordersdirected respectively toward corresponding detectors and sources.
 8. Theimaging system of claim 6, wherein the optical element comprises apolarizing element.
 9. The imaging system of claim 8, further comprisinga circular polarizer disposed between the optical system and thepolarizing element so as to produce polarization components along botheigenaxes of the polarizing element.
 10. The imaging system of claim 6,wherein the sources emit light at a first wavelength, the detectorsrespond to light at a second wavelength different from the firstwavelength, and the energy splitting element comprises a refractiveelement.
 11. The imaging system of claim 1, wherein the optical systemis disposed with respect to the source array and the detector array sothat some points on the object plane of the optical system producerespective images at the image plane that encompass a detector and asource corresponding thereto.
 12. The imaging system of claim 1, whereinthe optical system comprises a microscope.
 13. The imaging system ofclaim 12, further comprising an optical element disposed between theoptical system, on the one hand, and the detectors and sources, on theother hand, to produce conjugate points in image space coupledrespectively to corresponding sources and detectors.
 14. The imagingsystem of claim 13, wherein the energy splitting element comprises adiffractive element optimized to maximize energy in diffraction ordersdirected respectively toward corresponding detectors and sources. 15.The imaging system of claim 13, wherein the optical element comprises apolarizing element.
 16. The imaging system of claim 15, furthercomprising circular polarizer disposed between the optical system andthe polarizing element so as to produce polarization components alongboth eigenaxes of the polarizing element.
 17. The imaging system ofclaim 13, wherein the sources emit light at a first wavelength, thedetectors respond to light at a second wavelength different from thefirst wavelength, and the energy splitting element comprises arefractive element.
 18. The imaging system of claim 13, wherein theoptical system is disposed with respect to the source array and thedetector array so that some points on the object plane of the opticalsystem produce respective images at the image plane that encompass adetector and a source corresponding thereto.
 19. The imaging system ofclaim 13, wherein the microscope comprises a confocal microscope. 20.The imaging system of claim 19, further comprising an optical elementdisposed between the optical system, on the one hand, and the detectorsand sources, on the other hand, to produce conjugate points in imagespace coupled respectively to corresponding sources and detectors. 21.The imaging system of claim 20, wherein the optical element comprises adiffractive element optimized to maximize energy in diffraction ordersdirected respectively toward corresponding detectors and sources. 22.The imaging system of claim 21, wherein the optical element comprises apolarizing element.
 23. The imaging system of claim 22, furthercomprising a linear polarizer disposed between the optical system andthe polarizing element so as to produce polarization components alongboth eigenaxes of the polarizing element.
 24. The imaging system ofclaim 19, wherein the sources emit light at a first wavelength, thedetectors respond to light at a second wavelength different from thefirst wavelength, and the energy splitting element comprises arefractive element.
 25. The imaging system of claim 19, wherein theoptical system is disposed with respect to the source array and thedetector array so that some points on the object plane of the opticalsystem produce respective images at the image plane that encompass adetector and a source corresponding thereto.
 26. The imaging system ofclaim 13, wherein the microscope includes a diffractive element disposedon the detector side thereof and optimized to maximize efficiency inorders of diffraction corresponding respectively to correspondingdetectors and sources.
 27. The imaging system of claim 1, wherein theoptical system comprises an array of optical elements corresponding torespective detectors of the detector array, the optical elementsilluminating an object with light from respective sources of the sourcearray and producing respective images of the object at their respectivedetectors.
 28. The imaging system of claim 27, wherein correspondingdetectors and sources are coplanar with one another.
 29. The imagingsystem of claim 27, wherein the optical elements comprise microscopes.30. The imaging system of claim 29, further comprising optical elementsdisposed between corresponding microscopes, on the one hand, and theircorresponding detectors and sources, on the other hand, to produceconjugate points in image space coupled respectively to correspondingsources and detectors.
 31. The imaging system of claim 30, wherein theenergy splitting elements comprise diffractive elements optimized tomaximize energy directed respectively toward corresponding detectors andsources.
 32. The imaging system of claim 29, wherein the opticalelements comprise polarizing elements.
 33. The imaging system of claim3, further comprising circular polarizers disposed between themicroscopes and their respective Wollaston prisms so as to producepolarization components along both eigenaxes of the Wollaston prisms.34. The imaging system of claim 29, wherein the sources emit light at afirst wavelength, the detectors respond to light at a second wavelengthdifferent from the first wavelength, and the optical elements comprisesdirect view prisms.
 35. The imaging system of claim 29, wherein themicroscopes are disposed with respect to respective correspondingdetectors and sources so that a point on the object plane of amicroscope produces an image at the image plane of the microscope thatencompasses a detector and a source corresponding thereto.
 36. Theimaging system of claim 29, wherein the microscopes are confocalmicroscopes.
 37. The imaging system of claim 29, wherein the sourcesemit light at a first wavelength and the detectors respond to light at asecond wavelength different from the first wavelength forepi-fluoresence microscopy.
 38. The imaging system of claim 1, whereinthe sources emit light at a first wavelength and the detectors respondto light at a second wavelength different from the first wavelength forepi-fluoresence microscopy.
 39. An equalization system adopted for usewith an imaging system having a plurality of light detectors arranged ina detector array, a light source, and an optical system disposed withrespect to the light source and the detector array so as to illuminatean object with light from the light source and image the object on thedetector array, the equalization system comprising: a signalconditioning circuit for receiving and digitizing output signals from arespective set of a plurality of light detectors so as to produce arespective set of output values; and an equalizer system for equalizingsaid respective set of output values for a given amount of optical inputpower supplied to the detectors.
 40. The equalization system of claim39, combined with an epi-illumination imaging system for producing animage at said detector array.
 41. The equalization system of claim 40,wherein said light source comprises an array of individuallight-emitting sources corresponding to respective said light detectors.42. The equalization system of claim 39, combined with atrans-illumination imaging system for producing an image at saiddetector array.
 43. The equalization system of claim 42, wherein saidlight source comprises an array of individual light-emitting sourcescorresponding to respective said light detectors.
 44. The equalizationsystem of claim 42, wherein said light source comprises a single-axisillumination system.
 45. The equalization system of claim 44, whereinsaid light source includes an extended light emitting source.
 46. Theequalization system of claim 39, wherein said equalizer system isadapted to adjust one or more of said output values according to arespective error correction value so as to produce new respective valuesthat are substantially equal for said given amount of input power. 47.The equalization system of claim 46, wherein correction values are addedto one or more of said output values to correct for detector offsetvariances.
 48. The equalization system of claim 46, wherein one or moreof said output values are multiplied by correction values to correct fordynamic range variances.
 49. The equalization system of claim 39,wherein said signal conditioning circuit includes a set of amplifierscorresponding to said set of said plurality of light detectors whichapply gain to said output signals prior to digitization thereof, andsaid equalizing system provides correction signals to said amplifiersbased on said output values so as to equalize said output values forsaid given amount of input power.
 50. The equalization system of claim49, wherein said amplifiers are adapted to adjust their gain in responseto said correction signals.
 51. The equalization system of claim 49,wherein said amplifiers are adapted to adjust their output offset inresponse to said correction signals.
 52. The equalization system ofclaim 49, wherein said amplifiers are adapted to adjust their gain andoutput offset in response to said correction signals.
 53. Theequalization system of claim 49, further comprising a plurality ofanalog-to-digital converters for converting said outputs of saidamplifiers to digital form, said analog-to-digital converters beingadapted to receive said correction signals and adjust their offsets inresponse thereto so as to compensate for offset variances among saidplurality of light detectors.
 54. The equalization system of claim 39,wherein said light source comprises an array of individuallight-emitting sources corresponding to respective said light detectors,said equalization system further comprising a power supply adapted tosupply to a plurality illumination light sources corresponding to saidplurality of detectors respective amounts of power that have definiterelative magnitudes with respect to one another, said equalizer systembeing adapted to equalize said set of output values by adjusting therelative amounts of power applied to said set of said plurality of lightsources.
 55. The equalization system of claim 54, wherein saidequalizing system is adopted to provide correction signals to said powersupply based on said output values so as to adjust the relative amountsof power applied to said set of said plurality of light-emitting sourcesand to adjust one or more of said output values based on a respectiveerror correction value so as to produce new respective values that aresubstantially equal for said given amount of input power therebyequalize said output values.
 56. The equalization system of claim 54,wherein said signal conditioning circuit includes a set of amplifierscorresponding to said set of said plurality of light detectors whichapply gain to said output signals prior to digitization thereof, andsaid equalizer system is adapted to provide correction signals to saidpower supply based on said output values so as to adjust the relativeamounts of power applied to said set of said plurality of light-emittingsources and to provide correction signals to said amplifiers based onsaid output values so as to equalize said output values for said givenamount of input power.
 57. The equalization system of claim 56, whereinsaid equalizer is further adapted to add to one or more of said outputvalues respective error correction values so as to produce newrespective values that are substantially equal for said given amount ofinput power.
 58. The equalization system of claim 39, wherein saidequalizer system is adapted to cause said set of output values torepresent a non-linear response to light received by said respective setof said plurality of detectors.
 59. The equalization system of claim 39,wherein said equalizer system is adapted to add to one or more of saidoutput values a respective error correction value so as to produce newrespective values that are substantially equal for said given amount ofinput power.
 60. The equalization system of claim 39, wherein saidequalizer system is adapted to multiply one or more of said outputvalues a respective error correction value so as to produce newrespective values that are substantially equal for said given amount ofinput power.
 61. A method for providing epi-illumination in an imagingsystem, comprising: arranging in an array a plurality of light detectorsin back of the imaging system so as to receive an image produced by theimaging system; and arranging in an array a plurality of light sourcescorresponding to respective said light detectors so as to provideillumination in front of the imaging system.
 62. The method of claim 61,further comprising arranging the sources so as to be interspersed amongthe detectors.
 63. The method of claim 61, further comprising arrangingthe sources and the detectors in the same plane.
 64. The method of claim61, further comprising arranging the sources and the detectors indifferent planes.
 65. The method of claim 61, further comprisingproviding a plurality of detectors corresponding to one or more sources.66. The method of claim 61, further comprising providing a plurality ofsources corresponding to one or more detectors.
 67. The method of claim61, further comprising providing an optical element in back of theimaging system so as to produce conjugate points coupled respectively tocorresponding sources and detectors.
 68. The method of claim 66, whereinproviding an optical element comprises providing a diffractive opticalelement.
 69. The method of claim 66, wherein providing an opticalelement comprises providing a refractive optical element.
 70. The methodof claim 66, wherein the sources emit light at a first wavelength andthe detectors respond to a second, different wavelength, and providingan optical element comprises providing a dispersive optical element. 71.The method of claim 61, further comprising arranging the detectors andthe sources so that some points on the object plane of the opticalsystem produce respective images that encompass a detector and a sourcecorresponding thereto.
 72. The method of claim 61, further comprisingusing the imaging system as a microscope.
 73. The method of claim 72,further comprising providing an optical element in back of the imagingsystem so as to produce conjugate points coupled respectively tocorresponding sources and detectors.
 74. The method of claim 73, whereinproviding an optical element comprises providing a diffractive opticalelement.
 75. The method of claim 73, wherein providing an opticalelement comprises providing a refractive optical element.
 76. The methodof claim 73, wherein the sources emit, light at a first wavelength andthe detectors respond to a second, different wavelength, and providingan optical element comprises providing a dispersive optical element. 77.The method of claim 72, further comprising arranging the detectors andthe sources so that some points on the object plane of the opticalsystem produce respective images that encompass a detector and a sourcecorresponding thereto.
 78. The method of claim 72, further comprisingusing the imaging system as a confocal microscope.
 79. The method ofclaim 78, further comprising providing an optical element in back of theimaging system so as to produce conjugate points coupled respectively tocorresponding sources and detectors.
 80. The method of claim 79, whereinproviding an optical element comprises providing a diffractive opticalelement.
 81. The method of claim 79, wherein providing an opticalelement comprises providing a refractive optical element.
 82. The methodof claim 79, wherein the sources emit light at a first wavelength andthe detectors respond to a second, different wavelength, and providingan optical element comprises providing a dispersive optical element. 83.The method of claim 78, further comprising arranging the detectors andthe sources so that some points on the object plane of the opticalsystem produce respective images that encompass a detector and a sourcecorresponding thereto.
 84. The method of claim 61, further comprisingforming the imaging system from a plurality of discrete optical systemsarranged in an array so that corresponding sources and detectorscorrespond to a discrete optical system.
 85. The method of claim 84,further comprising arranging corresponding detectors and sourcescoplanar with one another.
 86. The method of claim 84, furthercomprising using the discrete optical systems as array microscope. 87.The method of claim 86, further comprising providing one or more opticalelements in back of the imaging system so as to produce conjugate pointscoupled respectively to corresponding sources and detectors.
 88. Themethod of claim 87, wherein providing one or more optical elementscomprises providing one or more diffractive optical elements.
 89. Themethod of claim 87, wherein providing one or more optical elementscomprises providing one or more refractive optical elements.
 90. Themethod of claim 87, further comprising arranging the detectors and thesources so that some points on the object plane of a discrete opticalsystem produce respective images that encompass a detector and sourcecorresponding thereto.
 91. The method of claim 86, further comprisingusing the imaging system as a confocal microscope.
 92. The method ofclaim 91, further comprising using the imaging system as aepi-fluorescence microscope.
 93. The method of claim 61, furthercomprises using the imaging system as an epi-fluorescence microscope.94. A method for equalizing the output values of a photo-electronicimaging system for said given amount of input power, comprising:supplying a given amount of input power to an illumination light sourcein a photo-electronic imaging system; receiving and digitizing outputsignals from a respective set of a plurality of light detectors in theimaging system so as to produce a respective set of output values; andequalizing said set of output values for said given amount of inputpower.
 95. The method of claim 94, wherein said equalizing said set ofoutput values for a given amount of input power comprises adding to oneor more of said output values a respective error correction value so asto produce new respective values that are substantially equal for saidgiven amount of input power.
 96. The method of claim 94, wherein saidequalizing said set of output values for a given amount of input powercomprises multiplying one or more of said output values a respectiveerror correction value so as to produce new respective values that aresubstantially equal for said given amount of input power
 97. The methodof claim 94, further comprising providing a set of amplifierscorresponding to said set of said plurality of light detectors forproviding gain to the output signals, wherein an error signal is appliedto the amplifiers based on said output values so as to equalize saidoutput values for the given amount of input power.
 98. The method ofclaim 97, wherein the error signal is applied so as to adjust the gainof the amplifiers and thereby equalize said output values for the givenamount of input power.
 99. The method of claim 97, wherein the errorsignal is applied so as to adjust the offset of the amplifiers andthereby equalize said output values for the given amount of input power.100. The method of claim 97, further comprising providing a set ofanalog-to-digital converters corresponding and responsive to theamplifiers, and wherein error signals are provided to theanalog-to-digital converters to adjust their respective offsets so as toequalize the output values there from.
 101. The method of claim 97,wherein the error signal is applied so as to adjust the gain and offsetof the amplifiers and thereby equalize said output values for the givenamount of input power.
 102. The method of claim 94, wherein supplying agiven amount of power to an illumination light source comprisessupplying to a set of individual light-emitting sources respectiveamounts of power that have definite relative magnitudes with respect toone another so as to equalize said output values.
 103. The method ofclaim 94, wherein said equalizing is adapted to produce a non-linearresponse to light received by said respective set of said plurality ofdetectors.